It has always worked for me in the past. It wont starve the pumps and you will never have to worry about the chemical not going through. The factory will tell you this as well.
Are your water ball valves on the bottom of the tank half way? This will fix this problem.
As far as your tri foam issue, Factory set is usually 30psi air and 60psi product. But you can adjust to your liking
Probably a little late responding to this but I just joined. Greg is right. The measurement eye is the diagonal one in the middle of the unit. If this eye is bad the unit will be placed out of service